Would there be any interest in a service similar to BitPay but instead of instantly converting bitcoins into fiat, it would instantly convert altcoins to bitcoins?

BitPay allows people with bitcoins to spend their money at places which would otherwise only accept fiat. To do this, it instantly converts the customer's bitcoins to fiat which it then passes onto the merchant. From the merchant's perspective, this allows them to receive the exact amount of fiat that they want and still get the positive publicity that comes with accepting Bitcoin. Since this conversion is instant, it is superior to accepting bitcoin and then converting the coins to fiat manually since it shields the merchant from volatility in the BTC/USD exchange rate.

Now, couldn't the exact same thing work with altcoins and BTC? Using such a service, someone with namecoins or litecoins would be able to spend their coins at a shop that would otherwise only accept BTC. One of the criticisms of altcoins is that there are hardly any merchants who accept them. This service would allow altcoins to be spent wherever bitcoins can be spent. Integrating this service with BitPay itself would allow anyone to spend their altcoins in virtually every shop in the world.